The shell is part of a turtle's skeleton and it is attached to the spine. Marine and freshwater turtles have flatter, softer and lighter shells, while land turtles often carry a much heavier domed shell, which causes their movement be slow. Terrestrial turtles have short, sturdy feet, and freshwater turtles have webbed feet with longer claws. Marine turtles, such as the endangered leatherback, have flipper-like limbs adapted for swimming.
Turtles do not have teeth, so they eat using their strong jaws. Water turtles have varied diets, according to their species. Green and black sea turtles are vegetarians, feeding on algae. Loggerhead sea turtles also eat crabs, mollusks, shrimps and specially jellyfish. Most freshwater turtles are omnivorous, eating plant and animal food sources, such as worms, larvae, small fish, grasses and algae. Land turtles eat shrubs, grasses, insects, fruits, roots, seeds and cactus.
Marine turtles are often found in coastal waters, bays and estuaries, but also in the open sea. They inhabit tropical and temperate coastal areas around the world. Freshwater turtles live in rivers, lakes and estuaries. Some species are adapted to tolerate low levels of salt and can live in brackish waters and mangroves. Land turtles prefer dry and warm to temperate climates. Some land turtles, such as Gopherus agassizii, inhabit deserts, tolerating temperatures as high as 140 degrees Fahrenheit.
Although all turtles lay eggs, their nesting habits can differ not only according to habitat, but also species. After mating, sea turtles come ashore to nest during the warmest months of the year. The leatherback turtle is an exception, nesting in fall and winter. Sea turtles dig a small hole where they lay their eggs, which can number 50 to 200, depending on the species. Freshwater turtles have a similar behavior but often lay fewer eggs. Land turtles also excavate their nest on the ground, often close to shrubs. Geochelone denticulata, from South America, uses decaying leaf material as a nest.